Gear manufacturers utilize various machining processes and corresponding tools to produce gears. Exemplary processes can include hobbing, shaping, milling, shear cutting and grinding. The process selected by the gear manufacturer can depend on the type of gear being machined and the tolerances within which the gear is produced. Other considerations in selecting the method can include the size of the gear, the configuration of integral sections or flanges, the quantity of gears to be produced, and gear-to-pinion ratio and costs.
As one example, internal gears have involute tooth profiles, which can be provided by casting, shaping with a formed tool or milling with a formed milling cutter. Furthermore, accurate internal gears can be produced with greater precision by a pinion-shaped cutter or Fellow's cutter. However, the Fellow's cutter still merely provides an approximation of an involute tooth profile. Moreover, the size of the Fellow's cutter can determine certain restrictions on the tooth proportions of the internal gear in its final orientation. For instance, if the cutter is too large, the tips of two or more teeth in the internal gear can be inadvertently trimmed as the cutter is fed to depth. For that reason, smaller special cutters can be utilized; however, if the cutter is too small, imperfect tooth forms can be developed on the internal gear in its final orientation. Thus, special cutters and special cutting systems may be required to produce an internal gear having only an approximate tooth profile.
The internal gear in its final orientation may be configured to have an operating pitch diameter during the manufacturing process that is disposed within its involute tooth profile, thus reducing the accuracy by which the gear is produced. In particular, the cutter may cut the gear in the blank orientation in opposite directions along different portions of the same tooth face. For that reason, the cutter may be stationary with respect to the tooth face when the point of contact is aligned with the operating pitch diameter. Furthermore, when the point of contact is disposed radially outward from the operating pitch diameter, the cutter may apply a force in one direction along the face of the tooth, and when the point of contact is disposed radially inward from the operating pitch diameter, the cutter may apply a force in the opposite direction along the same face of the tooth. Thus, the cutter may cut the gear in multiple directions along one face of the same tooth and apply a non-constant force that increases or decreases along the same tooth face, which can in turn produce an imprecise involute tooth profile that is not within specification requirements.
It is therefore desirable to provide a cutter that can utilize a generally constant cutting tool force to produce a precision internal gear.